#23636 cmux-next: fix the two Chief title reds from #23391

Fixes two base reds that came in with #23391 (reported by chief-sidebar):

• ChiefWorkspaceRowsTests.theTaskTitleDropsOnlyASubagentID: ChiefWorkspaceName.taskTitle trimmed blanks on both ends before looking for the aN · id, so "a3 · " became "a3 ·", the " · " match failed, and it returned "a3 ·" instead of nil. It now drops only the leading blanks before the match; the trailing ones still go after.
• ChiefSidebarItemTests.dedupedSessionNamesKeepTheirRoleAndNumber: the test still expected the internal a3 / a10 ids as row titles. #23391 hides those ids on purpose (Leo's ask), and an untitled lane reads "Subagent". The test now gives the lanes task titles and checks that they keep their subagent-number order.

Example failing run: https://github.com/manaflow-ai/cmux/actions/runs/39635743092/job/119347539209

No capture: a string helper and a test, with no visible change beyond the "a3 · " edge case.

Agent session: cosmic-gray

🤖 Generated with Claude Code

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Summary by cubic

Fixes two Chief title test failures that came in with #23391.

• ChiefWorkspaceName.taskTitle now drops only leading whitespace before matching the subagent id, so "a3 · " keeps its " · " marker and no longer returns "a3 ·" instead of nil.
• The deduped-session test now gives lanes task titles and checks their subagent-number order, instead of expecting the internal a3/a10 ids as row titles.